Forests and water — it’s surprising how little we know

A report out today by the National Academy of Sciences says that there’s a surprising amount we don’t know about how doing things like cutting down vast swaths of a forested watershed affects the water supply downstream.

This stream near Greenwater illustrates what they’re talkin’ aboutP-I/Gilbert Arias

Requested by the U.S. Forest Service and the Bureau of Reclamation — which have to make decisions all the time about forests and the water supply they provide — offers:

Recent increases in fire, insects, and disease in forests have spurred adoption of forest management practices, such as thinning and salvage logging, whose effects on hydrology have received little study. The hydrologic effects of many of the new management practices and (best management practices) have not been studied, and dynamic forest conditions make it important to understand how contemporary practices influence water resources.

I didn’t realize until I read the report that there’s a notion that cutting down the forest increases the water supply downstream. The panel, which included input from enviros and scientists and the timber industry (did I forget anybody? let’s just say all the sides are represented) addresses this idea:

While it is possible to increase water yield by harvesting timber, water yield increases from vegetation removal are often small and unsustainable, and timber harvest of areas sufficiently large to augment water yield can reduce water quality.

Climate change, cumulative effects, and more all need careful study if we’re to keep our forests producing the water supply we all need, the panel concluded:

Forests are essential for the sustainable provision of water to the nation. It is incumbent upon scientists, policymakers, land and water managers, and citizens to use the lessons of the past and apply emerging research, technology, and partnerships to protect and sustain water resources from forested landscapes.